Sheet conveyance apparatus and image forming apparatus

ABSTRACT

A sheet conveyance apparatus includes a moving unit configured to move a conveyance unit nipping the sheet in the width direction such that in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from a reference position by an amount which is greater than a first predetermined amount and less than or equal to a second predetermined amount, the moving unit to move the conveyance unit by a third predetermined amount which is less than or equal to the first predetermined amount, and to perform control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the second predetermined amount, to perform abnormality processing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveyance apparatus which conveys sheets and an image forming apparatus including the sheet conveyance apparatus.

2. Description of the Related Art

Conventionally, an image forming apparatus which forms an image on a sheet includes a width direction correction mechanism for correcting a position of the sheet in a direction perpendicular to a sheet conveying direction of the sheet (i.e., in a width direction).

Japanese Patent Application Laid-Open No. 2013-126914 discusses a width direction correction mechanism as follows. The width direction correction mechanism includes a detection unit which detects an end of the sheet in the width direction, and moves the sheet in the width direction based on a detection result of the detection unit. More specifically, Japanese Patent Application Laid-Open No. 2013-126914 discusses detecting the end of the sheet using a contact image sensor (CIS) and moving a registration roller pair nipping a sheet therebetween in the width direction by a displacement amount from a reference position. However, there is a limit (i.e., an upper limit) to an amount the registration roller pair is movable in the width direction.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a sheet conveyance apparatus includes a conveyance unit configured to nip and convey a sheet, a detection unit configured to detect an end of a sheet in a width direction perpendicular to a sheet conveying direction, a moving unit configured to move the conveyance unit nipping the sheet in the width direction, and a control unit configured to control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from a reference position by an amount which is greater than a first predetermined amount and less than or equal to a second predetermined amount, the moving unit to move the conveyance unit by a third predetermined amount which is less than or equal to the first predetermined amount, based on a detection result of the detection unit, and to perform control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the second predetermined amount, to perform abnormality processing based on a detection result of the detection unit.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sheet conveyance apparatus according to a first exemplary embodiment of the present invention as viewed from a front side of the apparatus.

FIG. 2 illustrates the sheet conveyance apparatus according to the first exemplary embodiment as viewed from a rear side of the apparatus.

FIGS. 3A and 3B illustrate details of a conveyance roller contact and separation mechanism according to the first exemplary embodiment.

FIG. 4 is a block diagram illustrating an image forming apparatus according to the first exemplary embodiment.

FIG. 5 is a flowchart illustrating processing performed by the image forming apparatus according to the first exemplary embodiment.

FIGS. 6A and 6B illustrate a conveyance diagram and a drive diagram according to the first exemplary embodiment.

FIG. 7 illustrates an entire configuration of the image forming apparatus according to the first exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS Configuration of Image Forming Apparatus

A first exemplary embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a schematic cross-sectional view illustrating a color digital printer as an example of an image forming apparatus in which a sheet conveyance apparatus according to the present invention is included.

Image forming units in the image forming apparatus will be described below. Referring to FIG. 7, surfaces of four photosensitive drums 101 a, 101 b, 101 c, and 101 d are uniformly charged by respective charging rollers 102 a, 102 b, 102 c, and 102 d. Yellow (Y), magenta (M), cyan (C), and black (K) image signals are respectively input to laser scanners 103 a, 103 b, 103 c, and 103 d. The laser scanners 103 a, 103 b, 103 c, and 103 d then irradiate the drum surfaces with laser beams according to the input image signals, neutralize the charges, and forms latent images.

Developing units 104 a, 104 b, 104 c, and 104 d respectively develop the latent images formed on the photosensitive drums with yellow, magenta, cyan, and black toners. Primary transfer rollers 105 a, 105 b, 105 c, and 105 d then sequentially transfer the toner images developed on each of the photosensitive drums onto an intermediate transfer belt 106, i.e., an image bearing member formed of an endless belt. A full-color toner image is thus formed on the intermediate transfer belt 106.

A sheet fed from one of sheet feed cassettes 111 and 112, i.e., sheet feed units, is conveyed by an upstream roller pair 115 towards a registration roller pair (i.e., a conveyance unit) 120. Further, a sheet fed from a manual sheet feed unit 113 is similarly conveyed towards the registration roller pair 120. The toner image on the intermediate transfer belt 106 is controlled so as not to cause misregistration between the sheet conveyed by the registration roller pair 120 and the image. A second transfer outer roller 109 then transfers the toner image onto the sheet. A fixing unit 110 heats and presses the toner image to fix it on the sheet. The sheet is discharged from a first discharge portion 119 a or a second discharge portion 119 b to outside of the apparatus main body.

Side regulating plates have functions for preventing skew and positional displacement in the width direction of the sheet which may occur when the sheet is fed. However, a small gap between each of the side regulating plates and the sheet may actually cause the skew and the positional displacement in the width direction of the sheet. Further, the skew and the positional displacement in the width direction of the sheet may occur while the fed sheet is being conveyed.

To solve such a problem, according to the present exemplary embodiment, a leading end of a conveyed sheet is caused to contact a nip portion of the registration roller pair 120 which is not rotating. The leading end of the sheet is then pushed against the nip portion along the longitudinal direction thereof while a loop is formed in the sheet, and the skew of the sheet is corrected. In such a case, it is necessary for the upstream roller pair 115 to convey the sheet so that the leading end of the sheet contacts the nip portion of the registration roller pair 120 and is positioned along the nip portion thereof.

A CIS 143, which is a detection unit for detecting the position of the sheet in the width direction (i.e., the direction perpendicular to the conveying direction), is arranged between the registration roller pair 120 and a secondary transfer unit 118. After the registration roller pair 120 starts conveying the sheet, the registration roller pair 120 is shifted (moved) in a thrust direction (i.e., the width direction) based on the detection result of the CIS 143. The position of the sheet in the width direction is thus corrected.

(Configuration and Mechanism of Registration Unit)

A sheet conveyance apparatus according to the present exemplary embodiment will be described below with reference to the drawings. A sheet conveyance apparatus 116 is arranged in a sheet conveyance path connecting the sheet feed cassettes 111 and 112 and the image forming units. FIG. 1 is a perspective view illustrating the sheet conveyance apparatus 116 as viewed from the front side.

Referring to FIG. 1, the sheet conveyance path near the registration roller pair 120 includes a conveyance upper guide 121 a and a conveyance lower guide 121 b which are integrally configured. The conveyance upper guide 121 a and the conveyance lower guide 121 b are arranged to guide the sheet conveyed from the upstream roller pair 115 to the nip portion of the registration roller pair 120.

The registration roller pair 120 includes an upper roller (i.e., a first roller) 120 a having a roller formed of polyacetal (POM) and a lower roller (i.e., a second roller) 120 b formed of a rubber roller and arranged facing the upper roller 120 a. A rotating shaft 120 s which integrally rotates with the lower roller 120 b is supported to be rotatable by the conveyance roller guide 121 b via a bearing. Further, the upper roller 120 a is supported to be rotatable via a plurality of bearings 122 a, 122 b, and 122 c.

The bearings 122 a, 122 b, and 122 c are respectively fixed to spring hook members 123 a, 123 b, and 123 c which are integrally provided on the conveyance upper guide 121 a, so that the bearings 122 a, 122 b, and 122 c do not move in the sheet conveying direction. Further, the bearings 122 a, 122 b, and 122 c are held to be movable in the direction in which they become separated from the lower roller 120 b. When springs (i.e., biasing units) 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f illustrated in FIG. 2 are then hooked in a U-shape to hook portions formed on the spring hook members 123 a, 123 b, and 123 c, the upper roller 120 a is pressed against the lower roller 120 b, and a sheet nipping force is applied. In other words, the springs apply the nipping force (i.e., a biasing force) to the registration roller pair 120.

A registration motor 61 illustrated in FIG. 1 generates a driving force for rotating the registration roller pair 120. An upstream roller driving motor 62 generates a driving force for rotating the upstream roller pair 115.

A shift mechanism (i.e., the moving unit) which moves the sheet in the width direction will be described below. The lower roller 120 b of the registration roller pair 120 is fixed to the rotation shaft 120S, and the rotation shaft 120S is fixed to the apparatus main body to be movable in the width direction. The upper roller 120 a and the lower roller 120 b thus collectively move in the width direction along with the movement of the rotation shaft 120S in the width direction.

A pinion gear 44 which is rotated by the driving force from a shift motor 43 translationally moves a rack 45. The rack 45 is rotatable in a rotational direction with respect to the rotation shaft 120S and is fixedly-supported in the width direction. As a result, the registration roller pair 120 is movable in the width direction, and thus the sheet held by the registration roller pair 120 can be moved in the width direction.

A tooth width of an idler gear 63 is made wider than a tooth width of an input gear 68, so that engagement between the gears is maintained even if the registration roller pair 120 and the input gear 68 move in the thrust direction, and thus the registration roller pair 120 can rotate. The CIS 143 detects the positional displacement in the width direction. Further, the CIS 143 is arranged anterior to an image transfer unit in the conveying direction. Furthermore, the CIS 143 is eccentrically-arranged from the center in the width direction because it is sufficient to detect only one end side of the sheet, even when the sheet is of a minimum width size or a maximum width size.

A separation mechanism (i.e., a releasing unit) 150 which separates the registration roller pair 120 against the biasing force of the springs 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f will be described below with reference to FIGS. 2, 3A, and 3B. FIG. 2 is a perspective view illustrating the sheet conveyance apparatus 116 as viewed from the rear side. FIG. 3A illustrates a contacted state of the registration roller pair 120, and FIG. 3B illustrates a separated state thereof.

The separation mechanism 150 separates the upper roller 120 a from the lower roller 120 b to cause the sheet nipping force to be zero (i.e., sheet is released).

The driving force from an contact/separation motor 151 is transmitted to a motor input gear 152, an idler gear 153, and a cam input gear 154, to drive a cam 155. The contact/separation motor 151, the motor input gear 152, the idler gear 153, the cam input gear 154, and the cam 155 are symmetrically arranged in the front side and the rear side of the apparatus main body. The driving force from the contact/separation motor 151 in the rear side is transmitted to the front side via a cam shaft 157.

Lengths to the outer surface of the cam 155 from a rotational center axis thereof are different depending on the position, and when a distance from the center axis to the outer surface of the cam 155 is minimum, the registration roller pair 120 is in the contacted state (refer to FIG. 3A). On the other hand, when the distance from the center axis to the outer surface of the cam 155 is maximum, the cam 155 pushes up a cam follower 156 so that the registration roller pair 120 is in the separated state (refer to FIG. 3B). The cam follower 156 is arranged to be rotatable coaxially as the upper roller 120 a, and the cam 155 is arranged to be rotatable coaxially as the lower roller 120 b. When the cam follower 156 is pushed up by the cam 155, the upper roller 120 a is separated from the lower roller 120 b. According to the present exemplary embodiment, a separation amount is 2 mm. Thus, according to the present exemplary embodiment, the cam 155 and the cam follower 156 configure the separation mechanism (i.e., the releasing unit) 150.

When the registration roller pair 120 is in the separated state, an area of 60 degrees is of a constant radius in a cam profile, and a torque applied on the cam 155 becomes approximately zero. As a result, the registration roller pair 120 is maintained in the separated state even if the contact/separation motor 151 is turned off to be stopped.

Further, the cam 155 is supported to be rotatable by the bearing with respect to the rotation shaft 120 s, and moves independently of the driving force from the registration motor 61. In other words, the cam 155 does not rotate even when the registration motor 61 rotates the rotation shaft 120 s.

The shift mechanism integrally moves the registration roller pair 120, the conveyance upper guide 121 a, the conveyance lower guide 121 b, the spring hook members 123 a, 123 b, and 123 c, the springs 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f, the cam 155, and the cam follower 156, in the width direction. The tooth width of the cam input gear 154 is set wide so that the engagement between the cam 155 and the cam input gear 154 is maintained even when the cam 155 has shifted. As a result, the driving force from the contact/separation motor 151 is transmitted from the cam input gear 154 to the cam 155 even when the cam 155 has shifted.

FIG. 4 is a block diagram illustrating the image forming apparatus. Referring to FIG. 4, a controller 50, which serves as a control unit, is connected to an operation unit 200 and a display unit 210 in the image forming apparatus. Further, the controller 50 is connected to the registration motor 61, the upstream roller driving motor 62, a shift motor (i.e., a driving source) 43, the contact/separation motor (i.e., a driving source) 151, a registration sensor 141, and the CIS 143. Furthermore, the controller 50 is connected to a read-only memory (ROM) and a random access memory (RAM). The controller 50 uses the RAM as a work memory and executes programs stored in the ROM and corresponding to the processing illustrated in FIG. 5. According to the present exemplary embodiment, a common display having the functions of the operation unit 200 and the display unit 210 may be used.

(Processing for Correcting a Positional Displacement in the Width Direction)

Next, The processing for correcting the positional displacement in the width direction of the sheet performed by the sheet conveyance apparatus 116 according to the present exemplary embodiment will be described.

According to the present exemplary embodiment, the controller 50 moves the registration roller pair 120 nipping the sheet in the width direction by controlling driving of the shift motor 43 based on the detection result of the CIS 143. The position of the sheet in the width direction is thus corrected. More specifically, the displacement between the position of the end of the sheet detected by the CIS 143 and the reference position (i.e., the position of the end to be the reference when forming the image on the sheet) is calculated as a correction amount of the positional displacement in the width direction. The reference position is set for each sheet size, and the controller 50 previously stores a table which associates each sheet size with the reference position of the end of the sheet in the width direction. The controller 50 then refers to the table according to the position of the end in the width direction detected by the CIS 143 and determines a shift amount of the registration roller pair 120 in the width direction of the sheet. The controller 50 thus shifts (moves) the registration roller pair 120 in the thrust direction (i.e., the width direction) by the positional displacement correction amount and corrects the position of the sheet in the width direction.

According to the present exemplary embodiment, a limit (i.e., an upper limit) is set to the movable amount of the registration roller pair 120 in the width direction (hereinafter referred to as an upper limit amount as appropriate) in view of space, the skew, and productivity. According to the present exemplary embodiment, the upper limit amount is set to 3 mm.

According to the present exemplary embodiment, control performed by the controller 50 in a case where displacement of the end of the sheet detected by the CIS 143 from the reference position is greater than 3 mm (i.e., upper limit amount), is characteristic. The control performed by the controller 50 will be described below according to three cases. Hereinafter, the distance between the position of the end of the sheet detected by the CIS 143 and the reference position of the CIS 143 will be referred to as a displacement X.

(1) A Case where 0≦Displacement X≦3 mm

In such a case, the controller 50 moves the registration roller pair 120 in the width direction by the displacement X. As a result, the position of the sheet in the width direction can be corrected.

(2) A Case where 3 mm (i.e., the First Predetermined Amount)≦Displacement X≦5 mm (i.e., the Second Predetermined Amount)

In such a case, the controller 50 moves the registration roller pair 120 in the width direction by 3 mm (i.e., the upper limit amount). In other words, if the displacement X slightly exceeds the upper limit amount (3 mm) (i.e., the displacement X is less than or equal to 5 mm), the controller 50 does not determines that a paper jam (i.e., a conveyance abnormality) has occurred, and continues to convey the sheet.

Further, in such a case, the controller 50 displays a warning on the display unit 210 included in the apparatus main body. Such a warning may be an alarm for prompting a user to correctly set the sheet.

This is because, if the image is slightly displaced in the width direction (according to the present exemplary embodiment, if the displacement is corrected by the upper limit amount, the displacement becomes less than or equal to 2 mm), such a displacement may be tolerable by the user. If the controller 50 determines that a conveyance abnormality has occurred and stops conveying the sheet in the apparatus main body, it may be more inconvenient for the user.

(3) A Case where 5 mm (i.e., Second Predetermined Amount)≦Displacement X

In such a case, the controller 50 determines that the conveyance abnormality (i.e., paper jam) has occurred, and stops all motors in the apparatus main body including the registration motor 61 (i.e., performs abnormality processing). In other words, if the displacement X has greatly exceeded the upper limit amount of 3 mm (i.e., the displacement X has exceeded 5 mm), the controller 50 determines that the conveyance abnormality has occurred and stops conveying the sheet for the following reasons.

If the sheet is greatly displaced in the width direction (according to the present exemplary embodiment, the displacement exceeds 2 mm even when the displacement is corrected by the upper limit amount), the sheet may be caught at a position along the conveyance path in a downstream side. If the sheet is caught in the conveyance path, it may damage the components of the apparatus main body.

Further, if the sheet is greatly displaced in the width direction, it is highly likely that the sheet may be greatly skewed at the same time. It is then most likely that quality of a printed product (i.e., the sheet after the image is formed) may be tolerable by the user.

If the sheet is greatly displaced and conveyed (e.g., outside of a detection area of the CIS 143), the controller 50 determines that the conveyance abnormality has occurred similarly as described above, and stops conveying the sheet.

FIG. 5 is a flowchart illustrating control performed by the controller 50. FIG. 6A is a conveyance diagram illustrating leading end positions and trailing end positions of sheets when the sheets are continuously conveyed. FIG. 6B is a drive diagram illustrating driving performed by the contact/separation motor 151 and the shift motor 43. In FIGS. 6A and 6B, time is indicated on a horizontal axis, and the positions of the sheets are indicated on a vertical axis.

In step S101, the user executes a print job from the operation unit 200 in the image forming apparatus or a computer 201 connected to the image forming apparatus directly or via a network. In step S102, upon executing the print job, the controller 50 starts feeding the sheet. In step S103, the upstream roller pair 115 conveys the sheet to the registration sensor 141.

In step S104, when the registration sensor 141 detects the conveyed sheet, the upstream roller pair 115 stops rotating and temporarily stops the sheet immediately before the nip portion of the registration roller pair 120. In step S105, after a predetermined time has elapsed, the controller 50 controls driving of the upstream roller drive motor 62 and starts rotating the upstream roller pair 115. The controller 50 then causes the leading end of the sheet to contact the registration roller pair 120 and the sheet to form a loop, and thus corrects the skew.

In step S106, the controller 50 restarts the registration roller pair 120 and the upstream roller pair 115 at the same time, and conveys the sheet downstream while maintaining the sheet in a skew-corrected state.

In step S107, the CIS 143 detects the position of the end in the width direction of the sheet which has been conveyed downstream by the registration roller pair 120. The controller 50 then calculates the displacement (i.e., displacement X) in the width direction of the position of the end of the sheet detected by the CIS 143 from the reference position.

In step S108, the controller 50 determines whether the calculated displacement X matches one of the above-described cases 1, 2, and 3. More specifically, the controller 50 determines whether the displacement X is less than or equal to 3 mm.

In a case where the calculated displacement X is 0≦displacement X≦3 mm (YES in step S108), the processing proceeds to step 109. In step S109, the controller 50 controls the shift motor 43 to move the registration roller pair 120 in the width direction by the displacement X. As a result, the sheet can be aligned with the reference position.

In a case where the calculated displacement X is 3 mm≦displacement X≦5 mm (NO in step S108, and YES in step S110), in step S111, the controller 50 controls the shift motor 43 to move the registration roller pair 120 in the width direction by 3 mm. Further, the controller 50 displays the warning on the display unit 210.

On the other hand, in a case where the calculated displacement X is 5 mm<displacement X (NO in step S110), the processing proceeds to step 112. In step S112, the controller 50 stops driving the driving sources in the apparatus main body including the registration motor 61, and displays on the display unit 210 a message indicating that jam processing will be performed.

In step S113, when a time T₄ has elapsed from starting the correction in the width direction, the controller 50 conveys the sheet, the position of which has been corrected, to the secondary transfer unit 118 and performs image transfer to the sheet. In step S114, after the leading end of the sheet has advanced a predetermined amount from the secondary transfer unit 118, the controller 50 causes the contact/separation motor 151 to separate the registration roller pair 120. The step corresponds to an operation time T₃ illustrated in FIG. 6B.

In step S115, the controller 50 determines whether there is a subsequent sheet. In a case where there is a subsequent sheet (YES in step S115), the processing proceeds to step S116. In step S116, the controller 50 drives the shift motor 43 by the same amount as the shift amount in step S108 in the opposite direction. As a result, the registration roller pair 120 returns to an initial position in the width direction (hereinafter, the processing will be referred to as a shift home position operation). The processing corresponds to the processing performed at the operation time T₅ illustrated in FIG. 6B. In step S117, the controller 50 causes the registration roller pair 120 to contact each other after the trailing end of the previous sheet has passed through the registration roller pair 120 and before the subsequent sheet reaches the registration roller pair 120. The processing corresponds to the operation time T₂ illustrated in FIG. 6B. In a case where there is no subsequent sheet (NO in step S115), the processing proceeds to step S118. In step S118, the controller 50 ends the print job.

As described above, according to the present exemplary embodiment, the controller 50 controls the shift motor 43 and the contact/separation motor 151 to perform as follows. The controller 50 moves the registration roller pair 120, which is nipping the sheet, from the initial position in the width direction and separates the registration roller pair 120. The controller 50 then controls the shift motor 43 and the contact/separation motor 151 and causes the registration roller pair 120 to move to the initial position in the width direction while the registration roller pair 120 is in the separated state.

The controller 50 performs the shift home position operation while the registration roller pair 120 is in the separated state for the following reason. A sheet interval T₁ (i.e., the time after the trailing end of the previous sheet passes through and before the leading end of the subsequent sheet reaches the registration roller pair 120) is shorter than the shift home position operation time T₅. In other words, there is not enough time to perform the shift home position operation after the trailing end of the previous sheet has passed through the registration roller pair 120 and before the leading end of the subsequent sheet reaches the registration roller pair 120.

In recent years, processing speed of the image forming apparatuses has become higher. Further, the skew correction mechanism as described in the present exemplary embodiment stops the sheet before the registration roller pair 120. Thus, a sheet interval T₁ is often set shorter. As a result, as described above, it is desirable to perform the shift home position operation before the trailing end of the previous sheet passes through the registration roller pair 120 while the registration roller pair 120 is in the separated state.

When the shift operation is performed, the trailing end of the sheet is often being nipped by a plurality of rollers (e.g., the upstream roller pair 115). If the shift operation is performed in such a state, the loop formed between the registration roller pair 120 and the upstream roller pair 115 becomes twisted, so that a force which swivels the sheet is applied in the registration roller pair 120. If the swiveling force then becomes greater than the nipping force of the registration roller pair 120, the skew of the sheet may become worse at the registration roller pair 120.

In general, a nipping pressure of the registration roller pair 120 is often set higher as compared to other conveyance rollers for correctly matching timing of the image and the leading end of the sheet, and for preventing slipping of the sheet when conveying the sheet. Further, it is desirable to set the nipping pressure as high as possible so that the twisting of the loop as described above does not cause slipping.

In particular, stiffness of a cardboard which has large grammage is high, so that a larger swiveling force is applied and slipping easily occurs. To solve such a problem, according to the present exemplary embodiment, the nipping pressure of the registration roller pair 120 is set to 4 kgf larger than a normal conveyance roller pressure 1 kgf. The nipping force of the registration roller pair 120 is thus comparatively high for a conveyance roller, so that when the registration roller pair 120 is separated, a large rubbing force is generated between a cam surface of the cam 155 and the cam follower 156.

Japanese Patent Application Laid-Open No. 2008-50069 discusses a technique in which the cam follower shifts together with the conveyance roller. However, if the cam does not shift, the rubbing force becomes a resisting force in a case where the shift home position operation is performed while the registration roller pair is in the separated state. As a result, a load torque caused by the shift motor increases and abrasion due to rubbing also increases, so that an appropriate roller separation amount may not be obtainable. Further, the shift mechanism is deformed by the rubbing force, so that shift accuracy may be lowered.

According to the present exemplary embodiment, the image forming apparatus includes the separation mechanism and the shift mechanism as described above. The rubbing force thus does not affect the shift home position operation.

More specifically, according to the present exemplary embodiment, the registration roller pair 120, the springs 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f, which apply the nipping pressure to the registration roller pair 120, the cam 155, and the cam follower 156 collectively shift. Further, according to the present exemplary embodiment, the cam profile is determined so that the registration roller pair 120 is maintained in the separated state even if driving of the contact/separation motor 151 is stopped, when the cam 155 is driven and the registration roller pair 120 is separated.

As a result, according to the present exemplary embodiment, there is no influence of the rubbing force caused by the springs 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f even if the shift home position operation is performed while the registration roller pair 120 is in the separated state. The results described below are thus obtained.

Since the torque necessary for the shift operation can be reduced, the size of the shift motor 43 can be decreased. Further, since deformation of the shift mechanism due to the rubbing force can be reduced, the shift accuracy can be improved.

Furthermore, inertia of the registration roller pair 120 is not small, and an acceleration torque and a deceleration torque when performing the shift operation tend to be large. According to the present exemplary embodiment, since there is no influence of the torque due to the rubbing force, the acceleration torque and the deceleration torque can be increased, and the time required for performing the shift operation can be reduced. As a result, the present exemplary embodiment is applicable to an image forming apparatus of higher productivity.

According to the present exemplary embodiment, the nipping force of the registration roller pair 120 can be set high. Slipping when conveying the sheet to the image forming unit and when performing the shift operation thus becomes less likely to occur, and image printing accuracy is improved.

According to the above-described exemplary embodiment, the registration roller pair arranged upstream of the image forming unit that forms the images on the sheets is described as an example of the conveyance roller pair which shifts in the width direction and separates. However, the present invention is not limited thereto. For example, the present exemplary embodiment may be applied to a sheet aligning apparatus which also includes the conveyance roller pair that performs correction in the width direction, and similar results may be obtained.

Further, according to the above-described exemplary embodiment, the tension springs 124 a, 124 b, 124 c, 124 d, 124 e, and 124 f are hooked in the U-shape. However, the present invention is not limited thereto, and the biasing unit which applies the nipping force to the conveyance roller pair may be a compression spring or a plate spring.

Furthermore, according to the above-described exemplary embodiment, when the displacement X is greater than 5 mm (i.e., the second predetermined amount), abnormality processing, in which the motors in the apparatus main body including the registration motor 61 are stopped, is performed. However, the abnormality processing is not limited to stopping conveyance of the sheet, and the controller 50 may perform the following processing as abnormality processing. Specifically, if the displacement X is greater than 5 mm (i.e., the second predetermined amount), conveyance of the sheet is continued. The location at which the sheet is discharged is then changed to another location from the location at which the sheet is discharged when the displacement X is less than or equal to 5 mm. For example, it is assumed that when the displacement X is less than or equal to 5 mm, the sheet on which the image is formed is set to be discharged to the first discharge portion 119 a. On the other hand, if the displacement X is greater than 5 mm (i.e., second predetermined amount), the sheet is discharged to the second discharge portion 119 b. The controller 50 displays such a setting on the display unit 210. The controller 50 forms the image which is the same as the image to be formed on the sheet in which the displacement X is greater than 5 mm on the subsequent sheet, and continues the print job.

Moreover, according to the above-described exemplary embodiment, in the case where 3 mm≦displacement X≦5 mm, the registration roller pair 120 is shifted in the width direction by the upper limit amount (i.e., 3 mm). However, the present invention is not limited thereto. In other words, in the case where 3 mm≦displacement X≦5 mm, the registration roller pair 120 may be shifted in the width direction by the amount less than or equal to the upper limit amount (i.e., the third predetermined amount), such as 2.9 mm.

Further, the upper limit amount may be changed according to the type of the sheet. For example, if the sheet is of low grammage, or the length of the sheet in the conveying direction is short, the upper limit amount may be set to 4 mm, which is greater than 3 mm.

The exemplary embodiment of the present invention has been described above using specific numerical values. However, the numerical values are to be changed as appropriate according to characteristics of the apparatus, and the present invention is not limited thereto.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2013-225587 filed Oct. 30, 2013, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A sheet conveyance apparatus comprising: a conveyance unit configured to nip and convey a sheet; a detection unit configured to detect an end of a sheet in a width direction perpendicular to a sheet conveying direction; a moving unit configured to move the conveyance unit nipping the sheet in the width direction; and a control unit configured to control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from a reference position by an amount which is greater than a first predetermined amount and less than or equal to a second predetermined amount, the moving unit to move the conveyance unit by a third predetermined amount which is less than or equal to the first predetermined amount, based on a detection result of the detection unit, and to perform control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the second predetermined amount, to perform abnormality processing based on a detection result of the detection unit.
 2. The sheet conveyance apparatus according to claim 1, wherein the third predetermined amount is the same amount as the first predetermined amount.
 3. The sheet conveyance apparatus according to claim 1, wherein the control unit stops driving the conveyance unit as the abnormal processing.
 4. The sheet conveyance apparatus according to claim 1, wherein the control unit controls, in the case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is less than or equal to the first predetermined amount, the moving unit to move the conveyance unit by the separated amount.
 5. The sheet conveyance apparatus according to claim 1, wherein the third predetermined amount is the same amount as the first predetermined amount, and wherein the control unit controls, in the case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is less than or equal to the first predetermined amount, the moving unit to move the conveyance unit by the separated amount.
 6. The sheet conveyance apparatus according to claim 1, wherein the control unit calculates a displacement amount of the position of the end of the sheet in the width direction detected by the detection unit from the reference position, and controls the moving unit based on the calculated displacement.
 7. The sheet conveyance apparatus according to claim 1, wherein the control unit displays, in the case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the first predetermined amount and less than or equal to the second predetermined amount, a warning on a display unit.
 8. The sheet conveyance apparatus according to claim 1, wherein the conveyance unit includes a registration roller pair configured to convey a sheet to an image forming unit, and wherein the reference position is a position to be a reference when the image forming unit forms an image on a sheet.
 9. A sheet conveyance apparatus comprising: a conveyance unit configured to nip and convey a sheet; a detection unit configured to detect an end of a sheet in a width direction perpendicular to a sheet conveying direction; a moving unit configured to move the conveyance unit nipping the sheet in the width direction; and a control unit configured to control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from a reference position by an amount which is less than or equal to a first predetermined amount, the moving unit to move the conveyance unit by the separated amount, configured to control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the first predetermined amount and less than or equal to a second predetermined amount, the moving unit to move the conveyance unit by the first predetermined amount, and configured to perform control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the second predetermined amount, to stop driving the conveyance unit, based on a detection result of the detection unit.
 10. The sheet conveyance apparatus according to claim 9, wherein the control unit calculates a displacement amount of the position of the end of the sheet in the width direction detected by the detection unit from the reference position, and controls the moving unit based on the calculated displacement.
 11. The sheet conveyance apparatus according to claim 9, wherein the control unit displays, in the case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the first predetermined amount and less than or equal to the second predetermined amount, a warning on a display unit.
 12. The sheet conveyance apparatus according to claim 1, wherein the conveyance unit includes a registration roller pair configured to convey a sheet to an image forming unit, and wherein the reference position is a position to be a reference when the image forming unit forms an image on a sheet.
 13. An image forming apparatus comprising: a conveyance unit configured to nip and convey a sheet; an image forming unit configured to form an image on the sheet conveyed by the conveyance unit; a detection unit configured to detect an end of a sheet in a width direction perpendicular to a sheet conveying direction; a moving unit configured to move the conveyance unit nipping the sheet in the width direction; and a control unit configured to control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from a reference position by an amount which is greater than a first predetermined amount and less than or equal to a second predetermined amount, the moving unit to move the conveyance unit by a third predetermined amount which is less than or equal to the first predetermined amount, based on a detection result of the detection unit, and configured to perform control, in a case where the position of the end of the sheet in the width direction detected by the detection unit is separated from the reference position by an amount which is greater than the second predetermined amount, to perform abnormality processing based on a detection result of the detection unit. 